Method for coating steel parts with enamel

ABSTRACT

A method for the direct application of enamel to steel parts consisting of coating the surface of the steel parts with a zinc layer of between 0.3 to 5 g/m2 before the enamel coating is applied over the zinc layer in order to suppress defects which occur in the surface of the steel parts and provide a longlasting enamel surface.

United States Patent [191 Kaup et al.

[451 Nov. 19, 1974 METHOD FOR COATING STEEL PARTS WITH ENAMEL [75] Inventors: Friedel Kaup, Gutersloh; Heinrich Warnke, Marienfeld, both of 211 Appl. No.: 232,515

[52] US. Cl. 117/70 C, 117/71 M, 117/129, 1 17/131 [51] Int. Cl B23p 3/00, C230 3/02 [58] Field of Search 117/70 C, 71 M, 131, 53, 117/129, 70 A [56] References Cited UNITED STATES PATENTS 2,786,782 3/1957 Zimmermann et al 117/70 C 3,031,331 4/1962 Aves et al. 117/70 C 3,471,413

10/1969 Hervort 117/70 A Twells 117/70 A 3,559,280 2/1971 Mailhiot et al 117/71 M 3,594,214 7/1971 Helwig et al. 117/71 M 3,600,221 8/1971 Hibbs 117/71 M 3,674,445 7/1972 Wlodek 117/71 M OTHER PUBLICATIONS Sears Roebuck Catalog, Spring & Summer 1960, Philadelphia, Pa., pp. 851.

Primary Examiner--William D. Martin Assistant Examiner-William R. Trenor Attorney, Agent, or Firm-Allison C. Collard [5 7] ABSTRACT A method for the direct application of enamel to steel parts consisting of Y coating the surface of the steel parts with a zinc layer of between 0.3 to 5 g/m before the enamel coating is applied over the zinc layer in order to suppress defects which occur in the surface of the steel parts and provide a long-lasting enamel surface.

1 Claim, No Drawings METHOD FOR COATING STEEL PARTS WITH ENAMEL This invention relates to a method for a direct application of enamel to steel parts.

One of the disadvantages of coating steel parts directly with enamel is that defects appear on the surface of the coated steel parts if the steel has not been sufficiently decarbonized when they are submerged into the enamel slip. It is also known that, when the steel parts are to be protected during transportation, the steel manufacturer coats the steel parts with a zinc layer or coating. However, before the steel parts are coated with a layer of enamel, the zinc layer must be removed,

since it is generally believed that a perfect enameling of the steel parts is possible only after the zinc layer is removed. To remove the zinc layer before applying the enamel is expensive, and requires an additional operating step.

Accordingly, the present invention provides a method for coating steel parts with enamel which overcomes the above mentioned disadvantages by eliminating the need to remove the zinc layer or coating prior to the enameling step. In the invention, the surface of the steel parts are coated with a zinc layer of about 0.3 to g/m before the enamel coating is applied on the steel parts.

In another embodiment of the invention, a zinc layer is provided to protect the steel parts during transportation. Beforehand, the protective zinc layers have been removed from the steel parts before the enamel coating is applied, since it is generally assumed that the zinc layer would be a disabling factor during the enameling process. However, tests have shown that a zinc layer of 0.3 to 5 g/m surface improves the quality of the direct application of the enamel. If in the pre-treatment of the steel parts, i.e., the steel parts are already coated with a zinc layer of 0.3 to 5 g/m in surface area by the steel manufacturer in order to protect the parts during transportation and for the purpose of applying enamel directly, then the final process steps of enameling are reduced to a de-greasing, washing, and, if need be, a drying step before the enamel layer is applied.

When the enamel is directly applied, or applied by a conventional method, different methods of application may be used, such as for example submerging the steel parts in a slip. The term slip" is used herein to denote an enamel or glaze powdered and suspended in water, as defined in Websters 7th New Collegiate Dictionary, at page 820 (1965). As long as the enamel is of a dark shade color, such as black, dark blue, or brown, no problems arise with the submerging method. However, when light shaded colors, such as white enamel are used, dark spots may appear on the enamel surface.

This phenomenon is created by the following: When the pretreated steel parts are submerged into the slip, particles are removed from the surface of the steel parts which either intermix with the slip or form a thin film on the surface of the slip. In the first instance, these fine particles would be visible on the enamel. In the second instance, the particles would appear on the top of the enamel surface. Therefore, in both instances a defective surface would be obtained during the burning or firing process. Furthermore, the slip may become discolored so that it cannot be used further. The new method provides the following advantages:

1. Lower manufacturing costs due to the fact that the zinc layer does not have to be removed before the enamel is applied.

2. The goods do not have to be subjected to a drying process immediately after the enamel has been applied, since the zinc layer prevents the enamel from becoming discolored.

3. The shelf life of the goods is increased since the zinc layer covers the pretreated surface of the steel parts so that the influence of the atmosphere on the goods is reduced.

4. The surface quality of the goods is improved, because relatively smooth and abrasive resistant surfaces are provided before the enamel is applied.

5. Decarbonization defects in the steel are suppressed, because black spots, or so called needle points which would otherwise appear on the enamel surface are eliminated.

6. The slip does not discolor during the submerging step of the steel parts since the zinc layer on the steel parts provide a smooth and abrasive resistent surface. Furthermore, the zinc layer as well as zinc oxide and zinc hydroxide are white in color.

While only a few embodiments of the present invention have been shown and described, it will be obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.

What is claimed is:

1. Method for coating the surface of a steel article with an enamel coat, comprising the steps of:

a. applying to the steel surface a thin layer of metallic zinc having a thickness between about 0.3 and about 5 g/m to provide a smooth and abrasion resistant coat thereon;

b. immersing the zinc-coated steel surface in a liquid enamel slip to form a coating of the slip on the zinc layer, and, without drying; c. firing the slip to form an enamel outer coat on said steel article. 

1. METHOD FOR COATING THE SURFACE OF A STEEL ARTICLE WITH AN ENAMEL COAT, COMPRISING THE STEPS OF: A. APPLYING TO THE STEEL SURFACE A THIN LAYER OF METALLIC ZINC HAVING A THICKNESS BETWEEN ABOUT 0.3 AND ABOUT 5 G/M2 TO PROVIDE A SMOOTH AND ABRASION RESISTANT COAT THEREON; B. IMMERSING THE ZINC-COATED STEEL SURFACE IN A LIQUID ENAMEL SLIP TO FORM A COATING OF THE SLIP ON THE ZINC LAYER, AND, WITHOUT DRYING; C. FIRING THE SLIP TO FORM AN ENAMEL OUTER COAT ON SAID STEEL ARTICLE. 